296 SEALE. 



IV. THE PHILIPPINE WINDOW-SHELL. 

 DESCBIPTION. 



In the majority of windows in the city of Manila, the pane is of shell 

 instead of glass. The shell used for this purpose is called hapas or 

 window-shell {Placuma placenta Linn.). 



This shell (Plate VII, fig. 3) is thin and ilat with a rounded outline, 

 and somewhat resembles a very" large wafer. The entire shell including 

 the animal is about 1 centimeter in thickness (Plate VII, fig. 1) by 14 

 centimeters in diameter. The left side (valve) of the shell is slightly 

 convex, the right side is flat. The right side is easily transformed into 

 a windowpane simply by squaring off the edges with a big pair of scissors 

 or a crude machine such as is used for cutting plug tobacco. The shells 

 are then framed and are ready for use. The size of shell most in demand 

 will square 7.5 centimeters, although those that square 6.5 centimeters 

 are also much used. The opinion prevailing among the general public 

 regarding window-shell is that it is a slab of shell split ofE from some 

 larger shell. This, needless to say, is entirely erroneous, as the window- 

 shell is used in its natural condition, the two halves being torn apart 

 and the edges merely trimmed. The left side of the shell is convex and 

 hence is in but small demand. Windows made of these shells are trans- 

 lucent, admitting a soft light, very grateful to the eyes in a tropical 

 country. 



The windows present a most attractive appearance (see Plate IX, 

 fig. 1) and consequently are used in some of the handsomest structures 

 in Manila, such as the American Cathedral, the new General Hospital, 

 and the new Young Men's Christian Association building; and' while 

 they increase considerably the beauty of this type of architecture, they 

 are also peculiarly adapted to, and make a most attractive appearance in, 

 buildings of the bungalow style. 



DUBABILITT AND STRENGTH OF THE WINDOW-SHELL. 



These windows of shell last for generations. Some of the old churches 

 of Manila have shell windows which have been exposed to the weather for 

 over a hundred years and which are still serviceable. Shell windows are 

 easily repaired, as a new shell is readily sprung into place when one 

 becomes broken or worn. 



The sti-ength of these thin, wafer-like shells is something, astonishing. 

 Below is given a table showing the relative strength of window-sheU as 

 compared with plate glass 2_ to 3 millimeters in. thickness by actual test 

 in the Bureau of Science.® It is shown by this table that window-shell 

 is much stronger than plate glass 3 millimeters in thickness. The' 



"The tests were made by W. C. Reibling of the laboratory of inorganic and 

 physical chemistry, Bureau of Science. 



